1. Field of the Invention
The present invention relates to novel compositions, elements and methods for producing direct positive images from photographic materials containing negative-working emulsions. In particular, it relates to photothermographic materials and processes for providing direct positive neutral and color images from negative-working emulsions having in association therewith certain stable free radical nitroxyl compounds.
2. Description of the Prior Art
It is well known to develop a latent image in a photothermographic element using thermal processing. After imagewise exposure, the resulting latent image in the photothermographic element is developed and, in some cases, stabilized, merely by uniformly heating the photothermographic element. Such materials and process are described, for example, in U.S. Pat. No. 3,152,904 of Sorensen et al, issued Oct. 13, 1964; U.S. Pat. No. 3,301,678 of Humphlett et al, issued Jan. 31, 1967; U.S. Pat. No. 3,392,020 of Yutzy et al, issued July 9, 1968; U.S. Pat. No. 3,457,075 of Morgan et al, issued July 22, 1969; British Pat. No. 1,131,108, published Oct. 23, 1968; German Pat. No. 888,045, issued June 29, 1943, and British Pat. No. 1,161,777, published Aug. 20, 1969. Certain photothermographic materials for producing a developed image in color are also known, as described, for example, in U.S. Pat. Nos. 3,531,286 of Renfrew, issued Sept. 29, 1970, and 3,761,270 of deMauriac et al, issued Sept. 25, 1973. The described patents of deMauriac et al and Renfrew indicate that a color-forming coupler can be useful in a photothermographic material for producing a color image.
Copending U.S. Application Ser. No. 642,928 of cerquone et al, filed Dec. 22, 1975, now U.S. Pat. No. 4,021,240 photothermographic and thermographic elements, compositions and processes for providing a developed image in color. There is no teaching or suggestion in this application of using free radical nitroxyl compounds in such materials to obtain direct-positive images.
Copending U.S. Application Ser. No. 662,403 of Mowrey and Oftedahl, filed Mar. 1, 1976, now abandoned relates to an activator sheet for a dry thermal silver dye bleach process. This application also fails to teach or suggest the present invention.
Gabrielson et al, in copending U.S. Application Ser. No. 726,085, filed Sept. 23, 1976, now abandoned disclose the use of an azomethine or azo dye reducing agent and a negative-working silver halide photocatalyst in a photothermographic element to form a positive dye image which can be transferred to a receiving element or can remain in the element.
U.S. Pat. No. 3,589,901 of Lyons, issued June 29, 1971, relates to a method of making direct positive recordings from images of graphic originals onto light sensitive heat-developable sheet materials comprising photosensitive silver halide catalysts, heat-sensitive oxidants and reductants, and a source of mercury ion.
Research Disclosure 11611, published Dec., 1973, discloses the use of a broad range of nitroxyl compounds in developer compositions for conventional silver halide photograhic elements.
U.S. Pat. Nos. 3,600,168 and 3,600,169, both of Lawton, both issued Aug. 17, 1971, disclose the use of stable free radicals, such as nitroxyls, in compositions for electrostatic light sensitive reproduction sheets. Chemical Abstracts, Volume 64, 1966, Abstract 198876, discloses the use of free radical nitroxyl compounds as antioxidants and ultraviolet light absorbers in polymeric materials. U.S. Pat. No. 3,322,542 (Ullman et al), issued May 30, 1967, teaches the use of nitroxides to stabilize polychromic compounds against molecular deterioration.
Nitroxyls are described as oxidants in image transfer units in U.S. Application Ser. No. 367,304 by Chang et al and now abandoned.
British Pat. No. 1,326,889 of Konishiroku, published Aug. 15, 1973 teaches the use of nitroxyl radicals as anti-fading agents in conventional color photographic materials. Konishiroku, however, does not teach or suggest the use of stable free radical nitroxyl compounds in photothermographic materials comprising negative-working emulsions to produce direct positive images.
My co-worker, S. J. Ciurca, Jr. and myself have disclosed in our copending Application Ser. No. 814,620, filed of even date herewith, entitled "Stable Free Radical Nitroxyl Bleaching Agents for Photographic Processes," the use of certain stable free radical nitroxyl compounds as bleaching agents in photothermographic materials to produce negative dye and silver images.
However, there is no prior art teaching or suggestion of a solution to the problem of producing direct positive neutral and color images by the thermal development of photothermographic materials containing negative-working silver halide emulsions.